RFR: 8288040: x86: Loom: Improve cont/monitor-count helper methods

[Aleksey Shipilev]

On Wed, 8 Jun 2022 15:21:55 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> When doing x86_32 port, I realized that cont helper methods are sensitive to `rsp`, which makes the usual trick of using a scratch register for `thread` dangerous. We can just lift the entire thread-acquisition business into the methods themselves. Related to that, we can also do the same thing for monitor-count helper methods, thus fully isolating them from the caller code. It would be even better after [JDK-8286957](https://bugs.openjdk.org/browse/JDK-8286957).
> 
> This does the shared code change, so that x86_32 port can hopefully continue as late enhancement after RDP1.
> 
> Additional testing:
>  - [x] Linux x86_64 fastdebug, `jdk_loom hotspot_loom`
>  - [x] Linux x86_32 fastdebug, `jdk_loom hotspot_loom`

Thanks for reviews! I'll integrate to fit JDK 19 rampdown date today.

-------------

PR: https://git.openjdk.java.net/jdk/pull/9086